PROJECT SUMMARY Despite the undeniable success of immunization, >2 million infants still die annually from infections. Birth is the most reliable point of healthcare contact and is thus an ideal time point to ensure widespread immunization. However, neonatal immunity is distinct from adult as it is attenuated after birth, such that neonatal vaccine responses are often impaired. In this context, there is an urgent need to develop new neonatal vaccines, to date a slow, risky and error-prone undertaking. To provide the molecular basis for such efforts and accelerate and de-risk future vaccine development, the NIAID/NIH has initiated the Human Immunology Project Consortium with a focus on applying unbiased, global molecular (OMIC) and immunophenotyping techniques to interrogate the human immune system and its response to challenges such as immunization. One objective of our proposal on systems biology for the identification of biomarkers of neonatal vaccine immunogenicity is to map changes in neonatal plasma and leukocyte proteomes across the first 7 days of life in response to immunization with (a) nothing ? i.e., delayed immunization to Day 7 to define ontogeny (change with age), (b) Hepatitis B vaccine (HBV) for which there is a clear correlate of protection, (c) Bacille Calmette-Gurin (BCG) vaccine, known to modify HBV action, or (d) (HBV + BCG). Additional data are generated by employing novel in vitro immunization platforms employing blood from the same study participants (Project 3). The proteome basal state and landscape changes will be correlated with changes in the transcriptome (Service Core 1) and immune phenotype/status (Project 2). Integrative bioinformatic analysis in Project 1 will identify basal and vaccine-induced patterns of gene expression, protein translation, and pathways associated with successful immunization. HIPC Core/Project data will be shared/analyzed via a robust Data Management Core. To support these efforts, the Proteomics Core will pursue the following Specific Aims, using samples collected in The Gambia (Clinical Core (CC)-Site 1) and Papa New Guinea (CC-Site 2), and/or generated in the Levy Laboratory at Boston Children's Hospital (Project 3): Specific Aim1: Characterize the basal, ontogenic and vaccine-induced state of the neonatal plasma proteome across the first 7 days of life. Specific Aim2: Characterize the basal, ontogenic and vaccine-induced leukocyte proteome from the same blood sample as the plasma samples. Specific Aim3. Validate HBV-induced proteomic signatures correlating with immunogenicity using targeted LC/MS Approaches on samples from validation cohorts at CC Sites 1 and -2. Overall our Proteomics Core will provide groundbreaking insight into vaccine-induced plasma and leukocyte proteome signatures that correlate with protection thereby informing future neonatal vaccine development.